Mobile communication system

ABSTRACT

A mobile communication system and method that includes a radio access system employing a first communication scheme supporting packet-switched communication and a radio access system employing a second communication scheme supporting both circuit-switched communication and the packet-switched communication. The mobile communication system is configured to switch between a first communication state and a second communication state realizing single radio voice call continuity (SRVCC). The first communication state is when a first mobile station visits the radio access system employing the first communication scheme, and performs voice communication with a second mobile station and packet communication by using packet-switched system. The second communication state is when the first mobile station visits the radio access system employing the second communication scheme, and performs voice communication with the second mobile station by using circuit-switched system, and performs packet communication with the second station by using the packet-switched system.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of and, thereby,claims benefit under 35 U.S.C. §120 to U.S. patent application Ser. No.13/389,654 filed on Feb. 9, 2012, which is a national stage applicationof PCT Application No. PCT/JP2010/063654, filed on Aug. 11, 2010, whichclaims priority to Japanese Patent Application Nos. 2009-187564 and2009-193716 filed on Aug. 12, 2009 and Aug. 24, 2009, respectively. Thecontents of the priority applications are incorporated by reference intheir entirety.

TECHNICAL FIELD

The present invention relates to a mobile communication system.

BACKGROUND ART

Conventionally, there has been known a mobile communication systemcapable of accommodating a 2G/3G radio access system and an LTE (LongTerm Evolution) radio access system.

With reference to FIG. 25 and FIG. 26, an operation will be described,in which a mobile communication system switches a state (a firstcommunication state) where a mobile station UE#1 performs voicecommunication (VoIP communication) with respect to a mobile station UE#2 via an LTE radio access system to a state (a second communicationstate) where the mobile station UE #1 performs voice communication(circuit-switched communication) with respect to the mobile station UE#2 via a 2G/3G radio access system, that is, an operation for realizing“SRVCC (Single Radio Voice Call Continuity)” defined in Non-PatentDocument 1 will be described.

In step 1 in FIG. 25, the LTE radio access system (Source E-UTRAN)transmits a switching preparation instruction for the voicecommunication of the mobile station UE #1 to an enhanced MSC/MGW(Enhanced MSC Server Media Gateway for SRVCC) via a node MME (MobilityManagement Entity, Source MME) (steps 3 to 5 a in FIG. 26).

In step 2 in FIG. 25, the enhanced MSC/MGW transmits a resourcepreparation instruction for circuit-switched communication to a mobileswitching center MSC (Mobile-service Switching Center, Target MSC) andthe 2G/3G radio access system (Target RNC/BS), thereby preparing aresource for the voice communication (circuit-switched communication) ofthe mobile station UE #1 in an interval between the enhanced MSC/MGW andthe 2G/3G radio access system (a switching destination) (steps 5 b, 5 c,8 a, 8 b, and 8 c in FIG. 26).

In step 3 a in FIG. 25, the enhanced MSC/MGW transmits a switchingrequest of a path of a VoIP media signal and a VoIP control signal to anode SCC AS (Service Centralization and Continuity Application Server)arranged in a home network of the mobile station UE #1 in IMS (IPMultimedia Subsystem) (step 9 in FIG. 26), and the node SCC AS transmitsthe switching request of the path of the VoIP media signal to the mobilestation UE #2.

Furthermore, in step 3 b in FIG. 25, the enhanced MSC/MGW notifies theLTE radio access system of the completion of the above-mentionedswitching preparation, thereby transmitting a switching instruction fromthe LTE radio access system to the 2G/3G radio access system to themobile station UE #1 (steps 12 to 14 in FIG. 26).

As a consequence, the VoIP media signal is switched from a state (afirst communication state) where the VoIP media signal is exchangedbetween the mobile station UE #1 and the mobile station UE #2 via theLTE radio access system, a node S-GW (Serving-Gateway), and a node P-GW(a PDN-Gateway) to a state (a second communication state) where the VoIPmedia signal is exchanged between the enhanced MSC/MGW and the mobilestation UE #2.

Furthermore, the VoIP control signal (SIP signal) is switched from astate (a first communication state) where the VoIP control signal isexchanged between the mobile station UE #1 and the mobile station UE #2via the LTE radio access system, the node S-GW, the node P-GW, and theIMS to a state (a second communication state) where the VoIP controlsignal is exchanged between the enhanced MSC/MGW and the mobile stationUE #2 via the IMS.

Thus, between the mobile station UE #1 and the enhanced MSC/MGW, asignal (hereinafter, referred to as a “circuit-switched signal”) incircuit-switched communication including circuit-switched data and acontrol signal is exchanged via the 2G/3G radio access system. Here, theenhanced MSC/MGW is configured to convert the circuit-switched signaland a combination of the VoIP media signal and the VoIP control signal.

In addition, U plane data (hereinafter, referred to as a “packetsignal”), other than the above-mentioned VoIP media signal and VoIPcontrol signal, is switched from a state (a first communication state)where the packet signal is exchanged between the mobile station UE #1and a packet communication network via the LTE radio access system, thenode S-GW, and the node P-GW to a state (a second communication state)where the packet signal is exchanged between the mobile station UE #1and the packet communication network via the 2G/3G radio access system,the node S-GW, and the node P-GW.

PRIOR ART DOCUMENT Non-Patent Document

-   Non-Patent Document 1: 3GPP TS23.216, V9.0.0

However, the above-mentioned mobile communication system has a problemin that in the case of the switching from the first communication stateto the second communication state, since a path switching request istransmitted to the mobile station UE #2, which is a communicationpartner of the mobile station UE #1, and the mobile station UE #2performs path switching, when the mobile station UE #1 and the mobilestation UE #2 visit networks different from each other, the timerequired for the switching may become long.

Another problem is that in the case of the above-mentioned switching,since a path switching process in the mobile station UE #1 and a pathswitching process in the mobile station UE #2 are performed in parallel,even when the path switching process in the mobile station UE #1 hasbeen completed earlier, since a state (steps 9 to 16 in FIG. 26) wherevoice communication is not possible between the mobile station UE #1 andthe mobile station UE #2 occurs until the path switching process in themobile station UE #2 is completed, handover delay may occur.

In addition, in the above-mentioned mobile communication system, whenthe mobile station UE #1 has performed roaming, since the IMS located inthe home network of the mobile station UE #1 and a circuit-switcheddomain (a 2G/3G core network and radio access system) located in avisited network of the mobile station UE #1 should perform theabove-mentioned switching in cooperation with each other, both the homenetwork of the mobile station UE #1 and the visited network of themobile station UE #1 should have SRVCC support capability which is anoptional function. Furthermore, it is necessary to perform a complicatedprocedure such as interworking tests or contract conclusion.

Moreover, in the above-mentioned mobile communication system, it may notbe possible to perform the switching from the second communication stateto the first communication state.

SUMMARY OF THE INVENTION

Therefore, the present invention has been achieved in view of theabove-described problems, and an object thereof is to provide a mobilecommunication system which can realize SRVCC capable of continuouslyperforming voice communication within a visited network of a mobilestation UE #1 even when a first communication state and a secondcommunication state are switched, and can solve problems of aconventional mobile communication system.

A first characteristic of the present invention is summarized as amobile communication system which is provided with a radio access systememploying a first communication scheme not supporting circuit-switchedcommunication, a mobile delivery network accommodating the radio accesssystem employing the first communication scheme, a radio access systememploying a second communication scheme supporting the circuit-switchedcommunication, a core network employing the second communication schemeand accommodating the radio access system employing the secondcommunication scheme, and a service control network, and which isconfigured to switch between a first communication state and a secondcommunication state; in a case of the first communication state, a firstmobile station visits the radio access system employing the firstcommunication scheme and configured to perform voice communicationbetween the first mobile station and a second mobile station, and theconfiguration is such that a VoIP media signal is exchanged via theradio access system employing the first communication scheme and aserving gateway device arranged in a visited network of the first mobilestation in the mobile delivery network and a VoIP control signal isexchanged via the radio access system employing the first communicationscheme, the serving gateway device, and the service control networkbetween the first mobile station and the second mobile station; and in acase of the second communication state, the first mobile station visitsthe radio access system employing the second communication scheme and isconfigured to perform voice communication between the first mobilestation and the second mobile station, the configuration is such that acircuit-switched signal is exchanged between the first mobile stationand a gateway device arranged in the core network employing the secondcommunication scheme via the radio access system employing the secondcommunication scheme, the VoIP media signal is exchanged between thesecond mobile station and the gateway device via the serving gatewaydevice, the VoIP control signal is exchanged between the gateway deviceand the second mobile station via the serving gateway device and theservice control network, and the gateway device converts thecircuit-switched signal and a combination of the VoIP media signal andthe VoIP control signal.

A second characteristic of the present invention is summarized as amobile communication system which is provided with a radio access systememploying a first communication scheme not supporting circuit-switchedcommunication, a mobile delivery network accommodating the radio accesssystem employing the first communication scheme, a radio access systememploying a second communication scheme supporting the circuit-switchedcommunication, a core network employing the second communication schemeand accommodating the radio access system employing the secondcommunication scheme, and a service control network, and which isconfigured to switch between a first communication state and a secondcommunication state; in a case of the first communication state, a firstmobile station visits the radio access system employing the firstcommunication scheme and configured to perform voice communicationbetween the first mobile station and a second mobile station, and theconfiguration is such that a VoIP media signal is exchanged via theradio access system employing the first communication scheme and aserving gateway device arranged in a visited network of the first mobilestation in the mobile delivery network and a VoIP control signal isexchanged via the radio access system employing the first communicationscheme, the serving gateway device, and the service control networkbetween the first mobile station and the second mobile station; and in acase of the second communication state, the first mobile station visitsthe radio access system employing the second communication scheme and isconfigured to perform voice communication between the first mobilestation and the second mobile station, the configuration is such that acircuit-switched signal is exchanged between the first mobile stationand the serving gateway device via the radio access system employing thesecond communication scheme, the VoIP media signal is exchanged betweenthe second mobile station and the serving gateway device, the VoIPcontrol signal is exchanged between the first mobile station and thesecond mobile station via the radio access system employing the secondcommunication scheme, the serving gateway device, and the servicecontrol network, and the serving gateway device converts thecircuit-switched signal and the VoIP media signal.

As described above, according to the present invention, it is possibleto provide a mobile communication system which can realize SRVCC capableof continuously performing voice communication within a visited networkof a mobile station UE #1 even when a first communication state and asecond communication state are switched, and can solve problems of aconventional mobile communication system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the entire configuration of a mobilecommunication system according to a first embodiment of the presentinvention.

FIG. 2 is a sequence diagram illustrating an operation of the mobilecommunication system according to the first embodiment of the presentinvention.

FIG. 3 is a sequence diagram illustrating an operation of the mobilecommunication system according to the first embodiment of the presentinvention.

FIG. 4 is a diagram illustrating an operation at the time of Attach orlocation registration in the mobile communication system according tothe first embodiment of the present invention.

FIG. 5 is a flowchart illustrating an operation of MME according to thefirst embodiment of the present invention.

FIG. 6 is a flowchart illustrating an operation of an enhanced MSC/MGWaccording to the first embodiment of the present invention.

FIG. 7 is a flowchart illustrating an operation of SGW according to thefirst embodiment of the present invention.

FIG. 8 is a flowchart illustrating an operation of the SGW according tothe first embodiment of the present invention.

FIG. 9 is a sequence diagram illustrating an operation of the mobilecommunication system according to the first embodiment of the presentinvention.

FIG. 10 is a sequence diagram illustrating an operation of the mobilecommunication system according to the first embodiment of the presentinvention.

FIG. 11 is a diagram illustrating the entire configuration of a mobilecommunication system according to a first modification of the presentinvention.

FIG. 12 is sequence diagram illustrating an operation of the mobilecommunication system according to the first modification of the presentinvention.

FIG. 13 is a sequence diagram illustrating an operation of the mobilecommunication system according to the first modification of the presentinvention.

FIG. 14 is a flowchart illustrating an operation of MME according to thefirst modification of the present invention.

FIG. 15 is a flowchart illustrating an operation of the MME according tothe first modification of the present invention.

FIG. 16 is a flowchart illustrating an operation of SGSN according tothe first modification of the present invention.

FIG. 17 is a flowchart illustrating an operation of SGW according to thefirst modification of the present invention.

FIG. 18 is a flowchart illustrating an operation of the SGW according tothe first modification of the present invention.

FIG. 19 is a flowchart illustrating an operation of the SGW according tothe first modification of the present invention.

FIG. 20 is a sequence diagram illustrating an operation of the mobilecommunication system according to the first modification of the presentinvention.

FIG. 21 is a sequence diagram illustrating an operation of the mobilecommunication system according to the first modification of the presentinvention.

FIG. 22 is a diagram illustrating the entire configuration of a mobilecommunication system according to a second modification of the presentinvention.

FIG. 23 is a diagram illustrating the entire configuration of a mobilecommunication system according to a third modification of the presentinvention.

FIG. 24 is a sequence diagram illustrating an operation of the mobilecommunication system according to the third modification of the presentinvention.

FIG. 25 is a diagram illustrating the entire configuration of aconventional mobile communication system.

FIG. 26 is a sequence diagram illustrating an operation of theconventional mobile communication system.

DETAILED DESCRIPTION

(Mobile Communication System According to First Embodiment of thePresent Invention) With reference to FIG. 1 to FIG. 10, a mobilecommunication system according to a first embodiment of the presentinvention will be described.

As illustrated in FIG. 1, the mobile communication system according tothe present embodiment includes an LTE radio access system, a 2G/3Gradio access system, a mobile delivery network, a 2G/3G core network, aservice control network, and a packet communication network.

The LTE radio access system includes a radio base station eNodeB (notillustrated), and the 2G/3G radio access system includes a radio basestation NodeB (BS) (not illustrated) and a radio access control stationRNC (not illustrated).

The mobile delivery network includes a node MME, a node S-GW (ServingGateway device), and a node P-GW. Here, the node MME and the node S-GWare arranged in a visited network of a mobile station UE #1, and thenode P-GW is arranged in a home network of the mobile station UE #1.

The 2G/3G core network includes a node MSC (a circuit mobile switchingcenter), a node SGSN (a packet mobile switching center), or an enhancedMSC/MGW (a gateway node). Here, the node MSC, the node SGSN, and theenhanced MSC/MGW are arranged in the visited network of the mobilestation UE #1.

The IMS includes a node P-CSCF (Proxy-Call Session Control Function), anode S-CSCF (Serving-Call Session Control Function), a node S/P-CSCF,and a node SCC AS.

In the mobile communication system according to the present embodiment,a VoIP media signal, a VoIP control signal, and a packet signal areexchanged as U plane data according to the mobile station UE #1.

The mobile communication system according to the present embodiment isconfigured to switch between a state (a first communication state) wherethe mobile station UE #1 performs voice communication (VoIPcommunication) with respect to the mobile station UE #2 via the LTEradio access system and a state (a second communication state) where themobile station UE #1 performs voice communication (circuit-switchedcommunication) with respect to the mobile station UE #2 via the 2G/3Gradio access system and the enhanced MSC/MGW. That is, it is possible torealize SRVCC.

In the first communication state, the mobile station UE #1 (a firstmobile station) visits the LTE radio access system, and is configured toperform the voice communication with respect to the mobile station UE #2(a second mobile station).

Furthermore, in the first communication state, configuration is suchthat between the mobile station UE #1 and the mobile station UE #2, theVoIP media signal is exchanged via the LTE radio access system, the nodeS-GW, and the node P-GW, and the VoIP control signal is exchanged viathe LTE radio access system, the node S-GW, the node P-GW, and the IMS.

Moreover, in the first communication state, configuration is such thatbetween the mobile station UE #1 and the packet communication network, apacket signal is exchanged via the LTE radio access system, the nodeS-GW, and the node P-GW.

Meanwhile, in the second communication state, configuration is such thatthe mobile station UE #1 visits the 2G/3G radio access system, andperforms the voice communication with respect to the mobile station UE#2.

Furthermore, in the second communication state, configuration is suchthat a 2G/3G circuit-switched signal is exchanged between the mobilestation UE #1 and the enhanced MSC/MGW via the 2G/3G radio accesssystem, the VoIP media signal is exchanged between the enhanced MSC/MGWand the mobile station UE #2 via the node S-GW and the node P-GW, andthe VoIP control signal is exchanged between the enhanced MSC/MGW andthe mobile station UE #2 via the node S-GW, the node P-GW, and the IMS.

Moreover, in the second communication state, configuration is such thatbetween the mobile station UE #1 and the packet communication network,the packet signal is exchanged via the 2G/3G radio access system, thenode SGSN, the node S-GW, and the node P-GW.

In addition, the enhanced MSC/MGW is configured to convert a 2G/3Gcircuit-switched signal (a combination of a voice format and a controlsignal) and a combination of the VoIP media signal and the VoIP controlsignal.

With reference to FIG. 2 and FIG. 3, an operation of the mobilecommunication system according to the first embodiment of the presentinvention, specifically, an operation when the first communication stateis switched to the second communication state in the mobilecommunication system according to the first embodiment of the presentinvention will be described.

As illustrated in FIG. 2, in step S1000, since the current state is thefirst communication state, the U plane data including the VoIP mediasignal, the VoIP control signal, and the packet signal is exchangedbetween the mobile station UE #1 and the node P-GW via the radio basestation eNodeB and the node S-GW.

If a handover process of the mobile station UE #1 to the 2G/3G radioaccess system from the LTE radio access system starts between the mobilestation UE #1 and the radio base station eNodeB in step S1001, the radiobase station eNodeB transmits “Handover Required” to the node MME instep S1002.

In step S1003, the node MME determines whether the mobile station UE hasSRVCC-compatible capability and the node S-GW has predeterminedcapability (capability compatible with the present invention).

Here, the predetermined capability includes “capability to startBi-casting, which will be described later, when a predetermined triggerhas been detected”, or “capability to start the Bi-casting when uplink Uplane data is received via a radio access system which is a switchingdestination”.

When it is determined that the mobile station UE has theSRVCC-compatible capability and the node S-GW has the predeterminedcapability, the node MME transmits “Forward Relocation Request”including an IP address and TEID (Tunnel Endpoint Identifier) of thenode S-GW to the node SGSN in step S1004.

In step S1005, the node SGSN transmits “Relocation Request” includingthe IP address and the TEID of the node S-GW to the radio access controlstation RNC, and in step S1006, the radio access control station RNCtransmits “Relocation Request Acknowledge” to the node SGSN.

In step S1007, the node SGSN transmits “Forward Relocation Response”,which is addressed to the node S-GW, to the node MME.

The operations of step S1004 to step S1007 are operations according to ahandover process for a packet signal. That is, the handover process (aswitching process) for the packet signal according to the mobile stationUE #1 is performed via the node SGSN.

The node MME transmits “PS to CS Request” including the IP address andthe TEID of the node S-GW to the enhanced MSC/MGW in step S1008, theenhanced MSC/MGW transmits “Rel/HO Request” including an IP address andTEID of the enhanced MSC/MGW to the radio access control station RNC insteps S1009, and the radio access control station RNC transmits “Rel/HOAck” to the enhanced MSC/MGW in step S1010.

The enhanced MSC/MGW assigns the IP address and the TEID of the enhancedMSC/MGW-side for designating a bearer (a bearer for VoIP communication)used for the transfer of the VoIP media signal and the VoIP controlsignal for the mobile station UE #1 in step S1011, and transmits “PS toCS Response” including bearer information including the assigned IPaddress and TEID of the enhanced MSC/MGW-side to the node MME in stepS1012.

In step S1013, the node MME transmits “Modify Bearer Request” forsetting the above-mentioned bearer information to the node S-GW, and instep S1014, the node S-GW transmits “Modify Bearer Response” to the nodeMME.

In addition, in step S1013, the “Modify Bearer Request” may betransmitted from the enhanced MSC/MGW to the node S-GW, and in stepS1014, the “Modify Bearer Response” may be transmitted from the nodeS-GW to the enhanced MSC/MGW.

In step S1015, the node S-GW starts an operation (that is, “theBi-casting”) for transmitting a downlink VoIP media signal and VoIPcontrol signal to the radio base station eNodeB, and transmitting theVoIP media signal and the VoIP control signal to the radio accesscontrol station RNC via the enhanced MSC/MGW and the node MSC.

The node MME sets a VoIP bearer signal and the VoIP control signal notto be transferred to the node SGSN in step S1021, and transmits“Handover Command” to the radio base station eNodeB in step S1022.

The radio base station eNodeB transmits “HO from E-UTRAN Command” to themobile station UE #1 in step S1024.

In step S1025, a procedure for establishing a radio access link isperformed between the mobile station UE #1 and the radio access controlstation RNC, and in step S1026, the mobile station UE #1 transmits“Handover to UTRAN Complete” to the radio access control station RNC. Instep S1027, the transmission of uplink U plane data to the radio accesscontrol station RNC from the mobile station UE #1 is possible.

As illustrated in FIG. 3, in the case in which “Direct Forwarding” isapplied, if downlink U plane data is received in step S1028, the radiobase station eNodeB transfers the downlink U plane data to the radioaccess control station RNC.

Meanwhile, in the case in which “Indirect Forwarding” is applied, if thedownlink U plane data is received in step S1028, the radio base stationeNodeB transfers the downlink U plane data to the radio access controlstation RNC via the node S-GW. Here, when “Direct Tunnel” is not used,the radio base station eNodeB transfers the downlink U plane data fromthe node S-GW to the radio access control station RNC via the node SGSN.

In step S10281, the radio access control station RNC transmits “Reloc/HOComplete” to the enhanced MSC/MGW, and in step S10282, “PS to CSComplete/Ack” is exchanged between the node MME and the enhancedMSC/MGW.

In step S10283, the VoIP media signal and the VoIP control signal areexchanged between the node P-GW and the enhanced MSC/MGW via the nodeS-GW, and the circuit-switched signal is switched to be exchangedbetween the mobile station UE #1 and the enhanced MSC/MGW via the radioaccess control station RNC. Here, the enhanced MSC/MGW performs codecconversion (RTP/AMR-Iu-UP/AMR) between the circuit-switched signal and acombination of the VoIP media signal and the VoIP control signal.

In addition, when the uplink VoIP media signal or VoIP control signal isreceived, the node S-GW stops the above-mentioned Bi-casting, that is,stops the transfer of the VoIP media signal or the VoIP control signaldirected to the radio base station eNodeB.

In step S1029, the radio access control station RNC transmits“Relocation Complete” to the node SGSN.

In step S1030, the node SGSN transmits “Forward Relocation Complete” tothe node MME, and in step S1031, the node MME transmits “ForwardRelocation Complete Acknowledge” to the node SGSN.

In step S1032, the node MME transmits “Modify Bearer Request” to thenode S-GW. Here, the node S-GW changes bearer information in response tothe received “Modify Bearer Request”, separates the VoIP media signaland the VoIP control signal from the packet signal, and changes atransfer destination.

In step S1033, the node S-GW transmits the “Modify Bearer Request” tothe node P-GW, and in step S1034, the node P-GW transmits “Modify BearerResponse” to the node S-GW.

In step S1035, the node S-GW transmits the “Modify Bearer Response” tothe node MME.

In step S1036, the packet signal is switched to be exchanged between thenode P-GW and the mobile station UE #1 via the node S-GW, the node SGSN,and the radio access control station RNC.

In step S1037, open control of a bearer for packet communication used inthe first communication state is performed between the mobile station UE#1 and the node MME.

Next, with reference to FIG. 4, an operation at the time of Attach orlocation registration in the mobile communication system according tothe first embodiment of the present invention will be described.

As illustrated in FIG. 4, if the mobile station UE #1 transmits “AttachRequest” or “Tracking Area Update Request”, which includes informationindicating the presence or absence of SRVCC-compatible capability, tothe node MME in step S101, the node MME determines whether the mobilestation UE #1 has the SRVCC-compatible capability based on the received“Attach Request” or “Tracking Area Update Request” in step S102.

When it is determined that the mobile station UE #1 has theSRVCC-compatible capability, the node MME selects a node S-GW having theabove-mentioned predetermined capability and instructs the node S-GW toset a bearer for the mobile station UE in step S103.

In step S104, the node MME transmits “Attach Accept” or “Tracking AreaUpdate Accept” to the mobile station UE #1.

Next, with reference to FIG. 5, an operation of the node MME accordingto the present embodiment will be described.

As illustrated in FIG. 5, if the “Handover Required” is received fromthe E-UTRAN in step S111, the node MME determines whether a bearer forthe VoIP bearer signal has been set with reference to QCI (QoS ClassIdentifier) and the like in step S112.

When it is determined that the bearer for the VoIP bearer signal has notbeen set, the node MME performs a handover process according to typicalpacket communication, which is not associated with an SRVCC process, instep S113.

When it is determined that the bearer for the VoIP bearer signal hasbeen set, the node MME determines whether the node S-GW is compatiblewith the present invention, that is, the node S-GW has predeterminedcapability (capability compatible with the present invention) in stepS114.

When it is determined that the node S-GW is not compatible with thepresent invention, the node MME performs a conventional SRVCC process instep S115.

When it is determined that the node S-GW is compatible with the presentinvention, the node MME transmits “PS to CS Request”, which includes abearer context provided with a predetermined flag indicating that SRVCCaccording to the present invention is performed, to the enhanced MSC/MGWin step S116.

Next, with reference to FIG. 6, an operation of the enhanced MSC/MGWaccording to the present embodiment will be described.

As illustrated in FIG. 6, if the “PS to CS Request” is received from thenode MME in step S121, the enhanced MSC/MGW starts a process for thebearer context included in the “PS to CS Request” in step S122, andperforms the conventional SRVCC process in step S123.

In step S124, the enhanced MSC/MGW determines whether the predeterminedflag has been set in the bearer context included in the “PS to CSRequest”.

When it is determined that the predetermined flag has been set, thepresent operation proceeds to step S125. When it is determined that thepredetermined flag has not been set, the present operation ends.

In step S125, the enhanced MSC/MGW assigns bearer information (an IPaddress and TEID) for communication between the enhanced MSC/MGW and thenode S-GW, and notifies the node MME of the bearer information through“PS to CS Response”.

Next, with reference to FIG. 7, an operation 1 of the node S-GWaccording to embodiments of the present invention will be described.

As illustrated in FIG. 7, the node S-GW receives “Modify Bearer Request”from the node MME in step S131, and receives the IP address and the TEIDof the enhanced MSC/MGW in step S132.

In step S133, the node S-GW assigns bearer information (an IP addressand TEID) for communication between the node S-GW and the enhancedMSC/MGW, and notifies the node MME of the bearer information through“Modify Bearer Response”.

In step S134, the node S-GW starts the Bi-casting of the VoIP mediasignal directed to the enhanced MSC/MGW and the radio base stationeNodeB.

Next, with reference to FIG. 8, an operation 2 of the node S-GWaccording to embodiments of the present invention will be described.

As illustrated in FIG. 8, if uplink U plane data is received in stepS141, the node S-GW determines whether the U plane data is U plane datafrom the enhanced MSC/MGW in step S142.

When it is determined that the U plane data is not the U plane data fromthe enhanced MSC/MGW, the node S-GW continues the Bi-casting of the VoIPmedia signal directed to the enhanced MSC/MGW and the radio base stationeNodeB in step S143.

Meanwhile, when it is determined that the U plane data is the U planedata from the enhanced MSC/MGW, the node S-GW stops the transfer of theVoIP media signal corresponding to the U plane data to the radio basestation eNodeB, that is, the Bi-casting of the VoIP media signaldirected to the enhanced MSC/MGW and the radio base station eNodeB instep S144.

Next, with reference to FIG. 9 and FIG. 10, an operation of the mobilecommunication system according to the first embodiment of the presentinvention, specifically, an operation when the second communicationstate is switched to the first communication state in the mobilecommunication system according to the first embodiment of the presentinvention will be described.

As illustrated in FIG. 9, in step S2000, since the current state is thesecond communication state, U plane data is exchanged between the mobilestation UE #1 and the node P-GW via the radio access control station RNCand the node S-GW.

If a handover process of the mobile station UE #1 to the LTE radioaccess system from the 2G/3G radio access system starts between themobile station UE #1 and the radio access control station RNC in stepS2001, the radio access control station RNC transmits “RelocationRequired” including “CS/PS HO bit” to the node SGSN in step S2002.

In step S2003, the node SGSN determines whether the mobile station UEand the node MME are compatible with the present invention.

When it is determined that the mobile station UE and the node MME arecompatible with the present invention, the node SGSN adds a bearercontext for a VoIP media signal in step S2004.

The radio access control station RNC transmits “Relocation Required” tothe node MSC in step S2005, the node MSC transmits “MAP Prepare HO req”to the enhanced MSC/MGW in step S2006, the enhanced MSC/MGW transmits“CS to PS Request” to the node SGSN in step S2007, and the node SGSNstarts to create an EPS bearer for the VoIP media signal according tothe mobile station UE #1 in step S2008.

In step S2009, the node SGSN transmits “Forward Relocation Request”including a VoIP media addition identifier to the node MME.

As described above, when “CS/PS HO bit” is included in the “RelocationRequired” received in step S2002, or when it coincides with apredetermined determination logic, the node SGSN receives the “CS to PSRequest” from the enhanced MSC/MGW and then transmits the “ForwardRelocation Request” to the node MME.

In addition, when the “CS to PS Request” is not received from theenhanced MSC/MGW for a predetermined period, the node SGSN may performonly a handover process according to conventional packet communication.

The node MME adds the bearer context for the VoIP media signal based onthe VoIP media addition identifier included in the received “ForwardRelocation Request” in step S2010, and transmits “Relocation Request” tothe radio base station eNodeB in step S2011.

In step S2012, the radio base station eNodeB transmits “RelocationRequest Acknowledge” to the node MME, and in step S2013, the node MMEtransmits “Modify Bearer Request” to the node S-GW.

The node S-GW assigns an IP address and TEID to a bearer for the VoIPmedia signal in step S2014, and transmits “Modify Bearer Response”including the IP address and the TEID to the node MME in step S2015.

In step S2016, the node MME transmits “Forward Relocation Response” tothe node SGSN, and in step S2017, the node SGSN transmits “CS to PSResponse” to the enhanced MSC/MGW.

The operations of step S2009 to step S2017 are operations according to ahandover process for a packet signal.

In step S2018, the enhanced MSC/MGW transmits “MAP Prepare HO ack” tothe node MSC.

In step S2019, the node S-GW starts the Bi-casting of the VoIP mediasignal directed to the enhanced MSC/MGW and the radio base stationeNodeB (the bearer for the VoIP media signal).

The node MSC transmits “Handover Command” to the radio access controlstation RNC in step S2111, and the node SGSN sets a VoIP bearer signalnot to be transferred to the node MME in step S2112, and transmits the“Handover Command” to the radio access control station RNC in stepS2113.

In step S2114, the radio access control station RNC transmits “HO fromUTRAN Command” to the mobile station UE #1.

In step S2115, a procedure for establishing a radio access link isperformed between the mobile station UE #1 and the radio base stationeNodeB, and in step S2116, the mobile station UE #1 transmits “Handoverto E-UTRAN Complete” to the radio access control station RNC.

As illustrated in FIG. 10, in step S2117, the transmission of uplink Uplane data to the radio base station eNodeB from the mobile station UE#1 is possible.

In the case in which the “Direct Forwarding” is applied, if downlink Uplane data is received in step S2118, the radio access control stationRNC transfers the downlink U plane data to the radio base stationeNodeB.

Meanwhile, in the case in which the “Indirect Forwarding” is applied, ifthe downlink U plane data is received in step S2118, the radio accesscontrol station RNC transfers the downlink U plane data to the radiobase station eNodeB via the node S-GW. Here, when the “Direct Tunnel” isnot used, the radio access control station RNC transfers the downlink Uplane data from the node S-GW to the radio base station eNodeB via thenode SGSN.

In step S2119, the U plane data is exchanged between the mobile stationUE #1 and the node P-GW via the radio base station eNodeB and the nodeS-GW.

Here, if an uplink VoIP media signal is received, the node S-GW stopsthe above-mentioned Bi-casting and opens the bearer for the VoIP mediasignal directed to the enhanced MSC/MGW.

In step S2120, the radio base station eNodeB transmits “RelocationComplete” to the node MME.

In step S2121, the node MME transmits “Forward Relocation Complete” tothe node SGSN, and in step S2122, the node SGSN transmits “ForwardRelocation Complete Acknowledge” to the node MME.

In step S2123, the node SGSN transmits “Modify Bearer Request” to thenode S-GW.

In step S2124, the node S-GW transmits the “Modify Bearer Request” tothe node P-GW, and in step S2125, the node P-GW transmits “Modify BearerResponse” to the node S-GW.

In step S2126, the node S-GW transmits the “Modify Bearer Response” tothe node SGSN.

In step S2127, a packet signal is switched to be exchanged between thenode P-GW and the mobile station UE #1 via the node S-GW and the radiobase station eNodeB.

In step S2128, open control of a bearer for packet communication used inthe second communication state is performed between the mobile stationUE #1 and the node SGSN, and in step S2129, open control of a bearer forcircuit-switched communication used in the second communication state isperformed between the mobile station UE #1 and the enhanced MSC/MGW.

In accordance with the mobile communication system according to thefirst embodiment of the present invention, a switching process of thefirst communication state and the second communication state can berealized within a visited network of the mobile station UE #1, aswitching time for which communication is not possible can be reduced,and the switching process can be performed without control by the IMS.

As a consequence, since the above-mentioned switching process can becompletely concealed for the home network of the mobile station UE #1and the mobile station UE #2, the IMS arranged in the home network ofthe mobile station UE #1 does not require the SRVCC-compatiblecapability, and a complicated procedure is not required between the homenetwork and the visited network of the mobile station UE #1.

Furthermore, in accordance with the mobile communication systemaccording to the first embodiment of the present invention, the secondcommunication state can be switched to the first communication state,and the opportunity to simultaneously use the packet communication andthe voice communication using the LTE radio access system is increased,resulting in the improvement of a service quality.

(First Modification)

With reference to FIG. 11 to FIG. 21, a mobile communication systemaccording to a first modification of the present invention will bedescribed. Hereinafter, the mobile communication system according to thefirst modification of the present invention will be described whilefocusing on the difference from the above-mentioned mobile communicationsystem according to the first embodiment.

As illustrated in FIG. 11, the mobile communication system according tothe present first modification is not provided with the enhancedMSC/MGW.

In the first communication state, configuration is such that between themobile station UE #1 and the mobile station UE #2, the VoIP media signalis exchanged via the LTE radio access system and the node S-GW.

Furthermore, in the first communication state, configuration is suchthat the VoIP control signal is exchanged via the LTE radio accesssystem, the node S-GW, and the IMS.

In the second communication state, configuration is such that thecircuit-switched signal is exchanged between the mobile station UE #1and the node S-GW via the 2G/3G radio access system, the VoIP mediasignal is exchanged between the node S-GW and the mobile station UE #2,and the VoIP control signal is exchanged between the mobile station UE#1 and the mobile station UE #2 via the 2G/3G radio access system, thenode S-GW, and the IMS.

Furthermore, in the second communication state, the node S-GW isconfigured to convert the circuit-switched signal and the VoIP mediasignal.

With reference to FIG. 12 and FIG. 13, an operation of the mobilecommunication system according to the present first modification,specifically, an operation when the first communication state isswitched to the second communication state in the mobile communicationsystem according to the present first modification will be described.

As illustrated in FIG. 12, in step S3000, since the current state is thefirst communication state, the U plane data including the VoIP mediasignal, the VoIP control signal, and the packet signal is exchangedbetween the mobile station UE #1 and the node P-GW via the radio basestation eNodeB and the node S-GW.

If a handover process of the mobile station UE #1 to the 2G/3G radioaccess system from the LTE radio access system starts between the mobilestation UE #1 and the radio base station eNodeB in step S3001, the radiobase station eNodeB transmits the “Handover Required” to the node MME instep S3002.

In step S3003, the node MME determines whether the mobile station UE hasSRVCC-compatible capability and the node S-GW has predeterminedcapability (capability compatible with the present invention).

When it is determined that the mobile station UE and the node S-GW havethe SRVCC-compatible capability, the node MME transmits “ForwardRelocation Request” to the node SGSN in step S3004.

When it is determined that a bearer for the VoIP media signal exists inan MM context in step S3005, the node SGSN transmits “RelocationRequest” to the radio access control station RNC in step S3006. In stepS3007, the radio access control station RNC transmits “RelocationRequest Acknowledge” to the node SGSN.

In step S3008, the node SGSN transmits “Relocation Request for Iu-UP”including a bearer identifier for the VoIP media signal to the radioaccess control station RNC, and in step S3009, the radio access controlstation RNC transmits “Bearer Establish” including the bearer identifierfor the VoIP media signal to the node SGSN.

The node S-GW assigns the IP address and the port number of the nodeS-GW-side to an Iu-UP bearer in step S3010, and transmits “BearerConfirm” to the radio access control station RNC in step S3011.

In step S3012, an initialization process of the Iu-UP bearer isperformed between the node S-GW and the radio access control stationRNC, and in step S3013, the radio access control station RNC transmits“Relocation Request Acknowledgement for Iu-UP” to the node SGSN.

As a consequence, the setting of the Iu-UP bearer in the radio accesscontrol station RNC is completed in step S3014A, and the setting of theIu-UP bearer in the node S-GW is completed in step S3014B.

In step S3015, the node SGSN transmits “Forward Relocation Response”,which is addressed to the node S-GW, to the node MME.

In step S3016, the node S-GW starts the Bi-casting of the VoIP mediasignal directed to the radio access control station RNC (the Iu-UPbearer) and the radio base station eNodeB (the bearer for the VoIP mediasignal). Here, the node S-GW performs codec conversion(RTP/AMR-Iu-UP/AMR) between the circuit-switched signal and the VoIPmedia signal.

The node MME sets the VoIP bearer signal not to be transferred to thenode SGSN in step S3021, and transmits “Handover Command” to the radiobase station eNodeB in step S3022.

The radio base station eNodeB transmits “HO from E-UTRAN Command” to themobile station UE #1 in step S3024.

In step S3025, a procedure for establishing a radio access link isperformed between the mobile station UE #1 and the radio access controlstation RNC, and in step S3026, the mobile station UE #1 transmits“Handover to UTRAN Complete” to the radio access control station RNC. Instep S3027, the transmission of uplink U plane data to the radio accesscontrol station RNC from the mobile station UE #1 is possible.

As illustrated in FIG. 13, the mobile station UE #1 transmits thecircuit-switched signal to the node S-GW via the radio access controlstation RNC (the Iu-UP bearer) in step S3028, and the node S-GW acquiresa VoIP media signal by performing a codec conversion process withrespect to the received circuit-switched signal in step S3029, andtransmits the VoIP media signal to the node P-GW in step S3030.

The node S-GW stops the above-mentioned Bi-casting in step S3031 becausethe uplink U plane data has been received, and transmits acircuit-switched signal to the mobile station UE #1 via the radio accesscontrol station RNC (the Iu-UP bearer) in step S3032.

In the case in which the “Direct Forwarding” is applied, if downlink Uplane data is received in step S3033, the radio base station eNodeBtransfers the downlink U plane data to the radio access control stationRNC.

Meanwhile, in the case in which the “Indirect Forwarding” is applied, ifthe downlink U plane data is received in step S3033, the radio basestation eNodeB transfers the downlink U plane data to the radio accesscontrol station RNC via the node S-GW. Here, when “Direct Tunnel” is notused, the radio base station eNodeB transfers the downlink U plane datafrom the node S-GW to the radio access control station RNC via the nodeSGSN.

In step S3034, the radio access control station RNC transmits“Relocation Complete” to the node SGSN.

In step S3035, the node SGSN transmits “Forward Relocation Complete” tothe node MME, and in step S3036, the node MME transmits “ForwardRelocation Complete Acknowledge” to the node SGSN.

In step S3037, the node MME transmits “Modify Bearer Request” to thenode S-GW.

In step S3038, the node S-GW transmits the “Modify Bearer Request” tothe node P-GW, and in step S3039, the node P-GW transmits “Modify BearerResponse” to the node S-GW.

In step S3040, the node S-GW transmits the “Modify Bearer Response” tothe node MME.

In step S3041, the VoIP control signal and the packet signal areswitched to be exchanged between the node P-GW and the mobile station UE#1 via the node S-GW, the node SGSN, and the radio access controlstation RNC.

Here, the VoIP media signal is switched to be exchanged between the nodeS-GW and the node P-GW, and the circuit-switched signal is exchangedbetween the mobile station UE #1 and the node S-GW via the radio accesscontrol station RNC. Here, the node S-GW performs codec conversion(RTP/AMR-Iu-UP/AMR) between the circuit-switched signal and the VoIPmedia signal.

In step S3042, open control of a bearer for packet communication used inthe first communication state is performed between the mobile station UE#1 and the node MME.

Next, with reference to FIG. 14, an operation 1 of the node MMEaccording to the present first modification will be described.

As illustrated in FIG. 14, if the “Handover Required” is received fromthe E-UTRAN in step S201, the node MME determines whether a bearer forthe VoIP bearer signal has been set with reference to QCI and the likein step S202.

When it is determined that the bearer for the VoIP bearer signal has notbeen set, the node MME performs a handover process according to typicalpacket communication, which is not associated with an SRVCC process, instep S203.

When it is determined that the bearer for the VoIP bearer signal hasbeen set, the node MME determines whether the mobile station UE #1 andthe node S-GW are compatible with the present invention, that is, themobile station UE #1 and the node S-GW have a predetermined function(function according to the present invention) in step S204.

When it is determined that the mobile station UE #1 and the node S-GWare not compatible with the present invention, the node MME performs aconventional SRVCC process in step S205.

When it is determined that the mobile station UE #1 and the node S-GWare compatible with the present invention, the node MME transmits“Forward Relocation Request”, which includes a bearer context providedwith a predetermined identifier indicating that SRVCC according to thepresent invention is performed, to the node SGSN in step S206.

Next, with reference to FIG. 15, an operation 2 of the node MMEaccording to the present first modification will be described.

As illustrated in FIG. 15, if the “Forward Relocation Response” isreceived from the node SGSN in step S211, the node MME determineswhether the bearer for the VoIP bearer signal has been set withreference to QCI and the like in step S212.

When it is determined that the bearer for the VoIP bearer signal has notbeen set, the node MME performs a handover process according to typicalpacket communication, which is not associated with an SRVCC process, instep S213.

When it is determined that the bearer for the VoIP bearer signal hasbeen set, the node MME does not set bearer information for the VoIPmedia signal in “Bearers Subject to Data Forwarding List” within“Handover command” to be transmitted to the E-UTRAN, in step S214.

Next, with reference to FIG. 16, an operation of the node SGSN accordingto the present first modification will be described.

As illustrated in FIG. 16, if the “Forward Relocation Request” isreceived from the node MME in step S221, the node SGSN starts a processfor the bearer context included in the “Forward Relocation Request” instep S222, and determines whether a predetermined identifier has beenset in the bearer context included in the “Forward Relocation Request”in step S223.

When it is determined that the predetermined identifier has been set,the operation proceeds to step S224. When it is determined that thepredetermined identifier has not been set, the operation proceeds tostep S225.

In step S224, the node SGSN instructs the radio access control stationRNC to set a bearer for circuit-switched communication, and performs ahandover process according to typical packet communication, which is notassociated with an SRVCC process.

In step S225, the node SGSN performs the handover process according tothe typical packet communication, which is not associated with the SRVCCprocess.

Next, with reference to FIG. 17, an operation 1 of the node S-GWaccording to the present first modification will be described.

As illustrated in FIG. 17, if the “Bearer Establish” is received fromthe radio access control station RNC in step S231, the node S-GW assignsthe IP address and the port number of the node S-GW-side to the Iu-UPbearer and stores the bearer for the VoIP media signal, which is subjectto codec conversion, in step S232.

In step S233, the node S-GW transmits “Bearer Confirm” including the IPaddress and the port number.

Next, with reference to FIG. 18, an operation 2 of the node S-GWaccording to the present first modification will be described.

As illustrated in FIG. 18, if the setting of the Iu-UP bearer iscompleted between the node S-GW and the radio access control station RNCin step S241, the node S-GW starts the Bi-casting of the VoIP mediasignal directed to the radio access control station RNC and the radiobase station eNodeB in step S242.

Next, with reference to FIG. 19, an operation 3 of the node S-GWaccording to the present first modification will be described.

As illustrated in FIG. 19, if the uplink U plane data is received instep S251, the node S-GW determines whether the U plane data is U planedata received via Iu-UP in step S252.

When it is determined that the U plane data is not the U plane datareceived via the Iu-UP, the node S-GW continues the Bi-casting of theVoIP media signal directed to the radio access control station RNC andthe radio base station eNodeB in step S253.

Meanwhile, when it is determined that the U plane data is the U planedata received via the Iu-UP, the node S-GW stops the transfer of theVoIP media signal corresponding to the U plane data to the radio basestation eNodeB, that is, the Bi-casting of the VoIP media signaldirected to the radio access control station RNC and the radio basestation eNodeB in step S254.

Next, with reference to FIG. 20 and FIG. 21, an operation of the mobilecommunication system according to the present first modification,specifically, an operation when the second communication state isswitched to the first communication state in the mobile communicationsystem according to the present first modification will be described.

As illustrated in FIG. 20, in step S4000, since the current state is thesecond communication state, the U plane data is exchanged between themobile station UE #1 and the node P-GW via the radio access controlstation RNC and the node S-GW.

If a handover process of the mobile station UE #1 to the LTE radioaccess system from the 2G/3G radio access system starts between themobile station UE #1 and the radio access control station RNC in stepS4001, the radio access control station RNC transmits “RelocationRequired” to the node SGSN in step S4002.

When it is determined that the mobile station UE and the node MME arecompatible with the present invention, the node SGSN starts to create anEPS bearer for a VoIP media signal in step S4003.

In step S4004, the node SGSN transmits “Forward Relocation Request”including a bearer identifier for the VoIP media signal to the node MME.

The node MME adds the bearer context for the VoIP media signal based onthe bearer identifier for the VoIP media signal included in the received“Forward Relocation Request” in step S4005, and transmits “HandoverRequest” to the radio base station eNodeB in step S4006.

In step S4007, the radio base station eNodeB transmits “Handover RequestAcknowledge” to the node MME, and in step S4008, the node MME transmits“Modify Bearer Request” to the node S-GW.

The node S-GW assigns an IP address and TEID to a bearer for the VoIPmedia signal in step S4009, and transmits “Modify Bearer Response”including the IP address and the TEID to the node MME in step S4010.

In step S4011, the node MME transmits “Forward Relocation Response” tothe node SGSN.

In step S4012, the node S-GW starts the Bi-casting of the VoIP mediasignal directed to the enhanced MSC/MGW and the radio base stationeNodeB (the bearer for the VoIP media signal).

The node SGSN sets a VoIP bearer signal not to be transferred to thenode MME in step S4021, and transmits “Handover Command” to the radioaccess control station RNC in step S4022.

In step S4023, the radio access control station RNC transmits “HO fromUTRAN Command” to the mobile station UE #1.

In step S4024, a procedure for establishing a radio access link isperformed between the mobile station UE #1 and the radio base stationeNodeB, and in step S4025, the mobile station UE #1 transmits “Handoverto E-UTRAN Complete” to the radio base station eNodeB.

In step S4026, the transmission of uplink U plane data to the radio basestation eNodeB from the mobile station UE #1 is possible.

As illustrated in FIG. 21, the mobile station UE #1 transmits the VoIPmedia signal and the VoIP control signal to the node S-GW via the radiobase station eNodeB (the bearer for the VoIP media signal) in stepS4028, and the node S-GW transmits the VoIP media signal to the nodeP-GW without performing a codec conversion process with respect to thereceived circuit-switched signal in step S4029.

The node S-GW stops the above-mentioned Bi-casting in step S4030 becausethe uplink U plane data has been received, opens the bearer for the VoIPmedia signal directed to the radio access control station RNC, andtransmits a circuit-switched signal to the mobile station UE #1 via theradio base station eNodeB (the Iu-UP bearer) in step S4031.

In the case in which the “Direct Forwarding” is applied, if downlink Uplane data is received in step S4032, the radio access control stationRNC transfers the downlink U plane data to the radio base stationeNodeB.

Meanwhile, in the case in which the “Indirect Forwarding” is applied, ifthe downlink U plane data is received in step S4032, the radio accesscontrol station RNC transfers the downlink U plane data to the radiobase station eNodeB via the node S-GW. Here, when the “Direct Tunnel” isnot used, the radio access control station RNC transfers the downlink Uplane data from the node S-GW to the radio base station eNodeB via thenode SGSN.

In step S4033, the radio access control station RNC transmits“Relocation Complete” to the node SGSN.

In step S4034, the node SGSN transmits “Forward Relocation Complete” tothe radio base station eNodeB, and in step S4035, the radio base stationeNodeB transmits “Forward Relocation Complete Acknowledge” to the nodeSGSN.

In step S4036, the node SGSN transmits “Modify Bearer Request” to thenode S-GW.

In step S4037, the node S-GW transmits the “Modify Bearer Request” tothe node P-GW, and in step S4038, the node P-GW transmits “Modify BearerResponse” to the node S-GW.

In step S4039, the node S-GW transmits the “Modify Bearer Response” tothe node SGSN.

In step S4040, a packet signal is switched to be exchanged between thenode P-GW and the mobile station UE #1 via the node S-GW and the radiobase station eNodeB.

In step S4041, open control of a bearer for packet communication used inthe second communication state is performed between the mobile stationUE #1 and the node SGSN, and in step S4042, open control of a bearer forcircuit-switched communication used in the second communication state isperformed between the mobile station UE #1 and the node S-GW.

(Second Modification)

With reference to FIG. 22, a mobile communication system according to asecond modification of the present invention will be described.Hereinafter, the mobile communication system according to the secondmodification of the present invention will be described while focusingon the difference from the above-mentioned mobile communication systemaccording to the first modification.

As described in FIG. 22, in the mobile communication system according tothe present second modification, configuration is such that the VoIPcontrol signal and the packet signal are exchanged by passing throughthe node SGSN.

Meanwhile, configuration is such that the circuit-switched signal isexchanged without passing through the node SGSN.

(Third Modification)

With reference to FIG. 23 and FIG. 24, a mobile communication systemaccording to a third modification of the present invention will bedescribed. Hereinafter, the mobile communication system according to thethird modification of the present invention will be described whilefocusing on the difference from the above-mentioned mobile communicationsystem according to the first embodiment.

As described in FIG. 23, the mobile communication system according tothe present third modification may be so configured such that, in thesecond communication state, the VoIP control signal includinginformation according to the IMS may be exchanged between the enhancedMSC/MGW and the node SCC AS arranged in the home network of the mobilestation UE #1 via the node P-CSCF provided in the visited network of themobile station UE #1 and the node S-CSCF arranged in the home network ofthe mobile station UE #1.

For example, configuration may be such that when the first communicationstate is switched to the second communication state, the enhancedMSC/MGW may notify the node SCC AS arranged in the home network of themobile station UE #1 of the information (for example, information onMS-ISDN, and the like) according to the IMS, thereby updating theinformation according to the IMS held by the node SCC AS.

Specifically, as illustrated in FIG. 24, when the first communicationstate is switched to the second communication state, the enhancedMSC/MGW transmits “SIP message for information update” including“STN-SR” and “SDP-MGW” to the node S-CSCF arranged in the home networkof the mobile station UE #1 via the node P-CSCF provided in the visitednetwork of the mobile station UE #1 in step S5001. The SIP message forinformation update, for example, includes “UPDATE” or “RE-INVITE”.

Here, the “STN-SR” indicates a switching process from the firstcommunication state to the second communication state, and the “SDP-MGW”indicates VoIP media information.

In step S5002, the node S-CSCF transmits the “SIP message forinformation update” including the “STN-SR” and the “SDP-MGW” to the nodeSCC AS arranged in the home network of the mobile station UE #1.

In step S5003, the node SCC AS updates the information according to theIMS held by the node SCC AS in response to the received “SIP message forinformation update”.

Furthermore, in such a case, the node SCC AS may be configured to notifythe enhanced MSC/MGW of the information according to the IMS, which isheld by the node SCC AS before the first communication state is switchedto the second communication state.

The characteristics of the present embodiment as described above mayalso be expressed as follows.

A first characteristic of the present embodiment is summarized as amobile communication system which is provided with an LTE radio accesssystem (a first communication scheme) not supporting circuit-switchedcommunication, a mobile delivery network accommodating the LTE radioaccess system, a 2G/3G radio access system (a second communicationscheme) supporting the circuit-switched communication, a 2G/3G corenetwork and accommodating the 2G/3G radio access system, and IMS (aservice control network), and is configured to switch between a firstcommunication state and a second communication state; in the case of thefirst communication state, a mobile station UE #1 (a first mobilestation) visits the LTE radio access system and is configured to performvoice communication between the mobile station UE #1 and a mobilestation UE #2 (a second mobile station), and the configuration is suchthat a VoIP media signal is exchanged via the LTE radio access systemand a node S-GW (a serving gateway device) arranged in a visited networkof the mobile station UE #1 in the mobile delivery network and a VoIPcontrol signal is exchanged via the LTE radio access system, the nodeS-GW, and the IMS between the mobile station UE #1 and the mobilestation UE #2; and in the case of the second communication state, themobile station UE #1 visits the 2G/3G radio access system and isconfigured to perform voice communication between the mobile station UE#1 and a mobile station UE #2, the configuration is such that acircuit-switched signal is exchanged between the mobile station UE #1and an enhanced MSC/MGW arranged in the 2G/3G core network via the 2G/3Gradio access system, the VoIP media signal is exchanged between theenhanced MSC/MGW and the mobile station UE #2 via the node S-GW, theVoIP control signal is exchanged between the enhanced MSC/MGW and themobile station UE #2 via the node S-GW and the IMS, and the enhancedMSC/MGW converts the circuit-switched signal and a combination of theVoIP media signal and the VoIP control signal.

In the first characteristic of the present embodiment, in the case ofthe second communication state, configuration may be such that betweenthe enhanced MSC/MGW and a node SCC AS arranged in the home network ofthe mobile station UE #1, a VoIP control signal including informationaccording to the IMS may be exchanged.

Furthermore, a second characteristic of the present embodiment issummarized as a mobile communication system which is provided with anLTE radio access system, a mobile delivery network, a 2G/3G radio accesssystem; a 2G/3G core network, and IMS, and which is configured to switchbetween a first communication state and a second communication state; inthe case of the first communication state, a mobile station UE #1 visitsthe LTE radio access system and is configured to perform voicecommunication between the mobile station UE #1 and a mobile station UE#2, the configuration is such that a VoIP media signal is exchanged viathe LTE radio access system and a node S-GW and a VoIP control signal isexchanged via the LTE radio access system, the node S-GW, and the IMSbetween the mobile station UE #1 and the mobile station UE #2; and inthe case of the second communication state, the mobile station UE #1visits the 2G/3G radio access system and is configured to perform voicecommunication between the mobile station UE #1 and a mobile station UE#2, the configuration is such that a circuit-switched signal isexchanged between the mobile station UE #1 and the node S-GW via the2G/3G radio access system, the VoIP media signal is exchanged betweenthe node S-GW and the mobile station UE #2, the VoIP control signal isexchanged between the mobile station UE #1 and the mobile station UE #2via the 2G/3G radio access system, the node S-GW, and the IMS, and thenode S-GW converts the circuit-switched signal and the VoIP mediasignal.

In the second characteristic of the present embodiment, in the case ofthe second communication state, configuration may be such that the VoIPcontrol signal may be exchanged between the mobile station UE #1 and themobile station UE #2 via the 2G/3G radio access system, a node SGSN (apacket mobile switching center) arranged in the 2G/3G core network, thenode S-GW, and the IMS.

It is noted that the operation of the above-described the MME, SGW, PGW,P-CSCF, S-CSCF, SCC, AS, S/P-CSCF, eNodeB, SGSN, MSC or UE may beimplemented by a hardware, may also be implemented by a software moduleexecuted by a processor, and may further be implemented by thecombination of the both.

The software module may be arranged in a storage medium of an arbitraryformat such as RAM (Random Access Memory), a flash memory, ROM (ReadOnly Memory), EPROM (Erasable Programmable ROM), EEPROM (ElectronicallyErasable and Programmable ROM), a register, a hard disk, a removabledisk, and CD-ROM.

The storage medium is connected to the processor so that the processorcan write and read information into and from the storage medium. Such astorage medium may also be accumulated in the processor. The storagemedium and processor may be arranged in ASIC. Such the ASIC may bearranged in the MME, SGW, PGW, P-CSCF, S-CSCF, SCC, AS, S/P-CSCF,eNodeB, SGSN, MSC or UE. Further, such a storage medium or a processormay be arranged, as a discrete component, in the MME, SGW, PGW, P-CSCF,S-CSCF, SCC, AS, S/P-CSCF, eNodeB, SGSN, MSC or UE.

Thus, the present invention has been explained in detail by using theabove-described embodiments; however, it is obvious that for personsskilled in the art, the present invention is not limited to theembodiments explained herein. The present invention can be implementedas a corrected and modified mode without departing from the gist and thescope of the present invention defined by the claims. Therefore, thedescription of the specification is intended for explaining the exampleonly and does not impose any limited meaning to the present invention.

1. (canceled)
 2. A mobile communication system comprising: a radioaccess system employing a first communication scheme supportingpacket-switched communication; a radio access system employing a secondcommunication scheme supporting both circuit-switched communication andthe packet-switched communication; and an IMS (IP Multimedia subsystem),wherein the mobile communication system is configured to switch betweena first communication state and a second communication state realizingsingle radio voice call continuity (SRVCC), characterized in thatwherein first communication state is that a first mobile station visitsthe radio access system employing the first communication scheme, andperforms voice communication with a second mobile station and packetcommunication by using packet-switched system, wherein secondcommunication state is that the first mobile station visits the radioaccess system employing the second communication scheme, and performsvoice communication with the second mobile station by usingcircuit-switched system, and performs packet communication with thesecond station by using the packet-switched system, and wherein themobile communication system switches from the first communication stateto the second communication state in a visited network of the firstmobile station.
 3. A mobile communication method in a mobilecommunication system that includes a radio access system employing afirst communication scheme supporting packet-switched communication, aradio access system employing a second communication scheme supportingboth circuit-switched communication and the packet-switchedcommunication; and an IMS (IP Multimedia subsystem), the methodcomprising: switching between a first communication state and a secondcommunication state realizing single radio voice call continuity(SRVCC), characterized in that wherein first communication state is thata first mobile station visits the radio access system employing thefirst communication scheme, and performs voice communication with asecond mobile station and packet communication by using packet-switchedsystem, wherein second communication state is that the first mobilestation visits the radio access system employing the secondcommunication scheme, and performs voice communication with the secondmobile station by using circuit-switched system, and performs packetcommunication with the second station by using the packet-switchedsystem, and wherein switching by the mobile communication system fromthe first communication state to the second communication state in avisited network of the first mobile station.